Buy an existing mold for testing...cheap...$12. Mix the epoxy very slowly (no air bubbles) or vacuum the bowl of epoxy to de-gas. pour. cure. It would be as smooth as a baby's ass.

Quote:

Originally Posted by craftycoder

I am not willing to spend the months necessary to become an expert at silicone mold making. Anyone who says you can make a perfect mold the first time is full of it. I know I will need to make 10 before I am satisfied and I just don't have the patience for that. I need to cast a couple dozen of these things and it would be nice if I didn't have to add $350 for a mold to the $500 I've got in each of these Motobrains before they ship. After a few dozen samples are out the door I expect purchase orders which will allow me to outsource the manufacturing and all these goofy failures will be but a distant memory.

Failures are part of the engineering process. I assure you that every other development project of this type ever attempted by man has encountered its share of problems. You guys are hearing about them because I am sharing the entire process with y'all but failures are absolutely part of the process. Normally I am excited by failures because they are learning experience (and I have a hard-on for learning) but in this case since I really don't care about casting and mold making it is just pain. No one ever promised this was going to be all Champagne and stinky cheese however, so I shall persevere.

I've got two more units I've promised to ship out ASAP and I hope the remaining mold I have will survive if I use a different release agent. At that point I'll try a new mold design. This time I will try a soft "silicone like" inner mold and a hard outer mold to support the Motobrain's weight and keep the silicone mold from splitting prematurely. Once I've draw up the new mold I'll post it up here for you guys to see.

I waxed up my remaining mold with some cheap floor wax and just finished casting another Motobrain. I am hoping that I can remove the Motobrain from the mold without destroying it (unlike the last two Motobrains I cast) so I can keep making these in the near term while I come up with a new silicone mold. You have collectively advised me to go ahead and figure how to work with silicone. I'm planning to try it out.

In other news, I've been refining the firmware and am really getting pleased with its function and reliability. I have heard also from the first recipient of a Motobrain and they are liking it so far. That is great news I'd say.

I finally have a little success in casting a Motobrain. The Motobrain looks great and the mold is intact! Unfortunately, I made two significant changes compared to the last attempt so I do not know for certain which change was responsible for the better outcome. I changed both the resin (because I ran out of the preferred resin) and the release agent. As I said last night, the release agent I used was cheap floor wax (and AquaNet hair spray). The resin is not preferred because it is harder and not thermally conductive. The customer I will send this unit to doesn't require high current capacity so I decided to make use of this resin rather than waste it.

I am still going to give a silicone mold a try but I won't have to wait on it which pleases me greatly!

I did another several hour test to see how a Motobrain cast in thermally conductive resin responds to high current loads. The test was similar to last one where I started at 50A and began taking regular readings and when I saw the temperature was stabilizing I turned it up 10A. The results are below. The maximum temps are much lower now than with the previous resin. This stuff is clearly allowing more heat to radiate off the device keeping the max temps in check (10 degrees lower inside and out with this resin compared to the previous) while also reducing the thermal gradients across the device which will improve MTBF in the long run.

The top was measured with the FLIR camera. The side was measured with a Fluke thermocouple. The internal was measured with a sensor on the MCU.

Here you can see the lab in the IR spectrum. The wires are straining under the current load. You can even see the two AC power lines I an running to the power supply to reduce the fire hazard.

This is a photo of the fake ignition switch I use. It is really a couple of series diodes that do a fine job convincing Motobrain that an alternator is running or not. All the current also flows through this and boy was it unhappy. 85C is HOT!

That is as hot as the Motobrain got over 2 hours of testing up to 90A.

I planned to do the test up to 100A but the power supply started to make "creaking" noises and I got nervous and shut it down. I am a bit intimidated by what Motobrain can do. 1300W is a ton of power! Still I did turn it up to 100A and took snap shot. It did the deed and didn't burst into flames. Kudos to you Motobrain. The internal temp was 44C.

I even did a little cold temperature testing. I put it in the freezer for 20 minutes and then powered her up to see what would happen. No drama at 4C. I'll need to do more of this but the preliminary testing I've done (down to -80C) has all been positive.

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I am going to make a silicone mold as the polypropylene mold has been a pain to work with. Most of the parts have been ordered. This is the master I've drawn up. It is much taller than is necessary, but it does allow me to make the pour a lot less of an exercise in dexterity. I can pour in the correct volume and then left gravity settle it down to the right volume. I am going to do it upside down and as fellow inmate Emerson Biguns first suggested and others have since followed. This allows me to put some heat sink features and a legend directly into the Motobrain which ought to be super cool at the end of the day. Not including the tabs, Motobrain is 3.5"x2.5"x1.5". The tabs can be sawed off.

I have been given lots of guidance on this process offline by someone who is willing help me out because he wants to be able to order his Motobrain already. You guys have been very generous with your attention and advice. Thank you for helping out!

I have been given lots of guidance on this process offline by someone who is willing help me out because he wants to be able to order his Motobrain already. You guys have been very generous with your attention and advice. Thank you for helping you!

Yep, Quite a few of us have been following and (trying to offering assistance throughout). It's been cool to see it come together and watch your dream live. You have taken it further then then probably most of us imagined.